A set of observations of independent variable $(x)$ and the corresponding dependent variable $(y)$ is given below.
$$\begin{array}{|c|c|} \hline
\text{x} & 5 & 2 & 4 & 3 \\ \hline \text{y} & 16 & 10 & 13 & 12 \\ \hline
\end{array}$$
Based on the data, the coefficient $a$ of the linear regression model $$y = a + bx$$ is estimated as $6.1$.
The coefficient $b$ is ____________________ (round off to one decimal place)